Sulfur dioxide extraction process



July 14, 1953 N. F. I INN ET A1.

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'iSv/1v embers Clbbornacqg July 14, 1953 N. F. I INN ETAL SULFUR DIOXIDE EXTRACTION PROCESS 2 Sheets-Sheet 2 Filed July l, l1950 25N meine? armado @mi JZormarz Ff Linn Hear* ErnsbdrlCcotb.

anverzbor Patented .uly 14, 1953 UNITED STATES PATENToFFicE Norman F. Linn, Summit, Henryl Ernst, Jr., Fanwood, and Arthur K. Scott, Westeld, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application Julyv 1, 1950, Serial No. 171,612

6 Claims. (Cl. 5802-40)- This invention concerns a process for the selective removal lofundesired constituents from hydrocarbon fractions by contacting such fractions with liquid sulfur dioxide. The invention resides in the provision of a greatly simplified process for separating sulfur dioxide from the mixtures of hydrocarbons and sulfur dioxide resulting from the contact. In accordance with this invention, rafiinate and extract streams, produced by the contacting of a feed stream with sulfur dioxide, are each puried in a simple system employing a reboiler type fractionator and a caustic Washing stage. The process is consequently operable with a minimum of processing equipment, and is characterized, for example, by elimination of manyv of the compressors and all of the evaporation stages ordinarily employed in the sulfur dioxide extraction process.

For many years it hasl been appreciated that certain hydrocarbon fractions obtained in the rening of petroleum could be upgraded by selective removal of aromatic hydrocarbon constituents. For example, the quality of kerosene as regards its burning characteristics may be greatly improved by the removal of aromatic hydrocarbons and sulfur containing hydrocarbons. Again, the viscosity index of lubricating oils', the cetane number of diesel fuels, and other properties may favorably be improved by removing undesired constituents from these petroleum fractions. In order to achieve these objectives a variety of treating processes have been suggested. One of these processes is a solvent extraction process employing liquid vsulfur dioxide to selectively extract the above mentioned constituents. The sul-p fur dioxide extraction process has been in commercial operation since about 1909. However, as conventionally practiced the process entails the useof extensiveplant facilities. It is the principal object of this invention to greatly simplify the commercial sulfur dioxide extraction processes in a manner exemplified by the material savings in processing equipment.

The manner in which this is achieved resides in the method employed for processing the raffinate and extract streams from the sulfur dioxide contacting step of the process. Heretofore, it has been considered a binding limitation to prevent heating of the extract and rafiinate streams to temperatures above about 300 F. For this reason, a separation of sulfur dioxide from the extract and rafiinate streams has been accomplished by a complicated multi-stage system of evaporators. It has nowvbeen found possible, by employing a reboiler type of fractionator operating at high pressure and by heating the extract and raflnate streams well above conventional temperatures, to effect substantially complete separation of sulfur dioxide from the extract or raffinate phase, in a single fractionation zone. This and other features of the present invention may be appreciated by reference to the accompanying drawings which diagrammatically illustrate a ow plan of an extraction process embodying the invention. Figure l of the drawings represents a portion of the process, while Figure 2 is a continuation of Figure l showing the remaining portion of the process.

Referring now to the drawings, a complete description of the present process will be given. At the same time operative temperature and pressure ranges will be given so as to exemplify a suitable manner of conducting this invention.

In the drawing the numeral l designates a treating tower in which liquid sulfur dioxide may be contacted with the hydrocarbon fraction which is to be treated. It may be assumed that the hydrocarbon fraction to be treated is a kerosene fraction. In fact the present process is of particular application to kerosene or diesel oil or,

` in other Words, to petroleum hydrocarbons boiling in the range of about 325 to 650 F., although the process may be applied to other fractions such as lubricating oils. A suitable feed stream, such as kerosene, is introduced to the system through line 2. It is to be understood that this stream has been dried so as to eliminate Water, and that the stream has also preferably been substantially deaerated. Conventional methods for eliminating air and water may be employed. As an example,

it is assumed that the feed stream of line 2 is at a temperature of about F., so that it is necessary to cool the stream to the treating temperature, for example, about 20 F., prior to introduction to treating tower I. The treating temperature is generally in the range of -10 F. to +40 F. For this purpose the feed stream may be passed through heat exchanger 3 in heat exchange relationship with rafnate from treatingY kerosene to about F. so that the kerosene may be removed from Chiller l6 through line I for introduction to the treating tower. Liquid sulfur dioxide is also Withdrawn from chiller 6 and is conducted through line -8 for introduction to treating tower I.

The sulfur Idioxide contacting tower I may be ofk conventional design, of a nature -to provide for the intimate contacting of the liquid sulfur dioxide, and the kerosene. As illustrated, this may be conducted in a countercurrent treating tower equipped with means for intimatelycontacting the two streams. For example, tower I may be filled with suitableH packing material,

such as Raschig rings, or otherinternal contacting means so that the kerosene movingup.-

wardly through the tower countercurrent to the sulfur dioxide moving downwardlythrough'the 4 may be carried out, depending upon a reboiler circuit to supply the remaining heat requirements of the fractionation. Thus, fractionator II will consist of a tower provided with sufcient plates to provide a total of about 4 or more theoretical plates. The ranate phase of line 4 is introduced to the fractionation zone at about the middle thereof, so that about the same number of plates are provided above the point of feed as are provided below the feed point. It is preferable that the entire fractionation be conducted in a zone operated at a pressure, well above atmospheric, for the purpose` I`I" at about 65 to150 p. s. i. g., a portion of the raiiinate phase will pass upwardly in the fracknown as the raffinate phaseA consisting princisist principally of sulfur dioxide together with.

constituents extracted `from the original hydrocarbon feed. Again, it is necessary in the processing of this stream that the hydrocarbons be separated from the sulfur-dioxide. 'Y

As indicated, therefore, ir'i'V the operation of a sulfur dioxide extraction'process, extract and raffinate phases are obtained consisting of hydrocarbon, sulfur dioxide mixtures. The particular novelty of this inventic'nrnv relates tothe manner in which thisseparation is accomplished. In essence the separation of sulfur'. dioxidefrom the raffinate phase Vis the same,-'in principle as the separation of sulfur dioxide from the extract phase. However, full detailsvoff'both of these separations will be given in'ordertofully. disclose the process of this invention. y

Referring iirst to the separation of sulfur dioxide from the raffinate phase, ythe raiinate phase removed from towerA I throughline (ImaY be passed through heat exchanger3 in the manner formerly indicated.A 'This' will be effective to raise the temperature ofthe raiiinate phase` from about 20 F.` to about 60 F. It is desirable that the rafiinate phase be heated to a considerably higher temperature, so that a preheater I0 is provided inline 4, effective to heat the. raffinate to a temperature of about 20 to 275 F. This will have the effect ofA convertingv most of the sulfur dioxide to vapor form, al'- though only a portionl ofthe hydrocarbonV constituents of the raffinate will be vaporized. Upon then introducing the heated raffinate phase of line 4 to fractionator II, effective"fractionation tionation zone as a vapor, While the greater portion will drop downwardly through the fractionation zone as a liquid. To balance' the heat requirements ofj thev fractionation, a, liquid stream is removedv from the bottom of' fractionator II. through line I2 and is passed' through the reboiler I3Y effective to raise the. temperature of thefstr'eam sufficiently to provide the necessary heat, necessitating heating to, about 40.0 to 500 F. V'In a typical case, the stream Vwithdrawn through line` I2 may be withdrawn at a temperature of about, 380 and' will be heated in reboiler I3. to.. a temperature of' about 455 E., after which it is thenjreturned to fractionator II through line I4j. This heating is suicient. to convert. the liquid material of lineV I2 toa. vaporousY material in line I4'. The vapors of line I4 rising through the lower subdivided portionof the. fractionator serve to strip substantially all sulfur dioxide from the liquid directed downwardly past the vapor' inlet I4` to be. removed through line I 5'.' The liquid bottoms product. of fractionator I'I", therefore, constitutes hydrocarbons. containing below about 0.002 moljfraction. of sulfur dioxide. The sulfur dioxide driven upwardly through the fractiona- This'. temperature is; suciently high to` permit` adverse. color degradation. ofy the hydrocarbons if maintained' for any very longperiod. For example,l materialv colorl degradation willoccur if the kerosene is maintained above about. 350 F. for as much as 10 minutes. In thev operation of the fractionator as. described., howeven, this is avoided' by limii'iirigY the average holdup time of the. hydrocarbons` at. the high` temperatures indicated to considerably, less, thanabout 10 minutes. This is. possible according to theprocess described, since about 30 to. '70%v of theheat, requirements ofthe fractionation are supplied by preheating the raflinate prior to introduction tofractionator I I. Consequently, the passage of liquid products through reboiler I3. to provide vthe remaining heat requirements may befconducted to maintain. thev holdup time-inthe-ifeboiiefcirouit te-wm-'fbepw 10 minutes, and in factto.',afewmseconds The raflinate of line I is completely processed by cooling in cooler l1 to` aftemperature ellow about 135 F. after which the'raiiinatef, Subjectedto a caustic wash'inI zne i8 to eliminate any traces of sulfur dioxide remaining. For this purpose the rafnatema'y be contacted with about to 35 per cent treat of 5 to10 B. caustic in the contacting zone. s;

rilhe sulfur dioxide, removed'frn fractio ator H through line l5 at a temperature of about 100 to 145 F., is conducted to a condenser 51 operated at a temperature and pressure to liquefy the sulfur dioxide. For example, if condenser 51 is operated at a temperature of about 110 F. and a pressure of 85 p. s. i. g., suitable liquefaction may be achieved. The liquid sulfur dioxide from condensate drum 58 may then be removed from this drum through line i9, for use in the process as required. Thus, sulfur dioxide of line I9 together with any makeup sulfur dioxide required introduced through line 20 may be conducted through line 2l through cooler 22 and thence to sulfur dioxide Chiller 6. Heat exchanger 22 is preferably operated to drop the temperature of the sulfur dioxide from about 110 F, to about 61 F. In sulfur dioxide chiller 6, operated at about 0.5 p. s. i. g., evaporation of a portion of the sulfur dioxide will occur effective to provide sufficient auto-refrigeration so as to cool the liquid sulfur dioxide to a temperature of about F. The liquid sulfur dioxide may then be withdrawn through line 8 for use in the process as formerly described. Vapors of sulfur dioxide produced during the auto-refrigeration, are removed from chiller 5 through line 24 at a temperature of about 15 F., and are conducted to compressor 25, operated to compress the sulfur dioxide to about 90 p. sl i. g., and to a temperature of about 267 F. This sulfur dioxide is then passed through line 26 and is cooled in heat exchanger 21 to a temperature of about 110 F., effective to cause liquefaction of the sulfur dioxide which may then be pumped to the sulfur dioxide storage drum 58 through line 28.

The remaining portions of the drawing relate principally to the manner in 'which the extract phase of line 9 is processed to separate the hydrocarbons therein from the sulfur dioxide which is the principal constituent of the extract phase. This separation is accomplished in a similar manner to that described in connection with lprocessing of the raffinate stream. Thus, the extract phase is passed through line 9, heat exchanger 22, and heat exchanger 30, so as to raise the extract from about F. to about 250 F. The extract is then introduced to a fractionator 3l similar to fractionator Il formerly described. However, fractionator 3l required about 5 or more theoretical plates, a greater number of the theoretical plates being above the extract phase feed input than below the feed input when the minimum number of plates are employed. The reboiler 32 is operated similarly to that associated with fractionator Il, although at a somewhat higher temperature level. For example, the liquid may be withdrawn from fractionator 3| through line 33 at a temperature of about 438 F. and may be converted to a vapor in line 34, at a temperature of about 487 F. As operated in this manner fractionator 3| will be effective to provide a liquid bottoms product containing less than about 0.002 mol fraction of sulfur dioxide, which may be removed by means of a caustic washapplied in zone35i-.operatedA similarlylto caustic wash zone IB. Again, it is preferred that prior to caustic wash the extract 'becooled `tea temperature below about .135 F.,Ibyu'se'of -the cooler 36. The sulfur dioxide obtainedloverhead from fractionator 3l at a temperature of. about F., will contain substantially no hydrocar-V bons and consequently can be conducted through linev 31 to condenser 51 and thence .to the liquid receiver 58. A portion of the sulfur dioxide is continuously, or periodically processed in a drying column 38 to veliminate any moisture present. Thus, aportion of the sulfur dioxide of -liner31 maybe introduced to the lower portion of a' fractionation zone 38 through line 39, while liquid sulfur: dioxide from line I9 is introduced to the topoflthe fractionator through line 40. The reboiler circuit lll is operated to provide the heat requirements necessary to permit removal of water from the bottom of fractionator 38 through line 42, and to permit removal of the dried sulfur dioxide from the top of the tower through line 43.

As heretofore described the process of this invention particularly concerns the manner in which extract and raffinate phases of a sulfur dioxide extraction unit are purified. As disclosed, each of these phases are to be preheated sufficiently to provide about 30 to 70% of the heat requirements of a single fractionation zone. The remaining heat requirements of the fractionation zone are provided by a reboiler circuit operated at temperatures above 400 F., and preferably above about 450 F. By providing at least 4 theoretical plates in the fractionation zone, it is possible to secure sharp fractionation between sulfur dioxide, and the hydrocarbons present in either the extract phase or the raiiinate phase. The hydrocarbons separated in the fractionation zone may then be completely purified by utilization of a caustic wash.

While this invention has been described with regard to use of a single fractionation zone for purifying extract or raninate phases, the principles of this invention may also be applied to a system employing two rather than one fractionation zones. In this case lower temperatures may be maintained in the reboiler circuits falling in the range of about 325 to 500 F. In this case it is also desirable to operate the second of the fractionation zones at a pressure of about atmospheric to 50 p. s. i. g.

What is claimed is:

1. In a process for the selective extraction of constituents from a hydrocarbon distillate in which the hydrocarbon distillate is contacted with liquid sulfur dioxide to provide extract and rainate streams, the improvement which comprises separately processing at least one of said streams as follows: pre-heating said stream to a temperature of at least about 200 F., passing said heated stream to at least one fractionation zone, withdrawing gas comprising sulfur dioxide from the top of the fractionation zone, cooling and condensing said sulfur dioxide and returning at least a portion of the liquefied sulfur dioxide to the fractionation zone as reflux, withdrawing liquid comprising hydrocarbons from the bottom of the fractionation zone and heating at least a portion of the said Withdrawn liquid to a temperature of about 400 to 500 F., and returning said heated portion to the bottom of the fractionation zone, said prooess being characterized by an average holdup time of the hydrocarbons at a temperature above 350 F. of less than 10 minutes.

2. The process defined by claim 1in which the said fractionation zone is maintained at about 65 to 150 p. s. i. g. f

3.. The process dened by claim 1 in which the said pre-heating of the said stream is suiiieient to supply about 30 to 70% of the heat requirements of the said fractionation.

4. The process defined by claim 1 in which the said hydrocarbon distillate constitutes a lubricating Oil,

5. The process dened by claim 1 in which the said hydrocarbon distillate constitutes kerosene.

6. The process dened by claim 1 in which vthe said hydrocarbon distillate constitutes diesel oil.

NORMAN F. LINN. HENRY ERNST. JR. ARTHUR K. SCOTT.

8 References cited in the me of this patent UNITED STATES PATENTS Number Number Name Date Ragatz Feb. 16, 1937 Thiele et al Feb. 23, 1937 Ragatz Jan. 2, 1940 FGREIGN PATENTS Country Date Great Britain Mar, 9, 1945 

1. IN A PROCESS FOR THE SELECTIVE EXTRACTION OF CONSTITUENTS FROM A HYDROCARBON DISTILLATE IN WHICH THE HYDROCARBON DISTILLATE IS CONTACTED WITH LIQUID SULFUR DIOXIDE TO PROVIDE EXTRACT AND REFFINATE STREAMS, THE IMPROVEMENT WHICH COMPRISES SEPARATELY PROCESSING AT LEAT ONE OF SAID STREAMS AS FOLLOWS: PRE-HEATING SAID STREAM TO A TEMPERATURE OF AT LEAST ABOUT 200* F., PASSING SAID HEATED STREAM TO AT LEAST ONE FRACTIONATION ZONE, WITHDRAWING GAS COMPRISING SULFUR DIOXIDE FROM THE TOP OF THE FRACTIONATION ZONE, COOLING AND CONDENSING SAID SULFUR DIOXIDE AND RETURNING AT LEAST A PORTION OF THE LIQUEFIED SULFUR DIOXIDE TO THE FRACTIONATIONZONE AS REFLUX, WITHDRAWING LIQUID COMPRISING HYDROCARBONS FROM THE BOTTOM OF THE FRACTIONATION ZONE AND HEATING AT LEAST A PORTION OF THE SAID WITHDRAWING LIQUID TO A TEMPERATURE OF ABOUT 400* TO 500* F., AND RETURNING SAID HEATED PORTION TO THE BOTTOM OF THE FRACTIONATION ZONE, SAID PROCESS BEING CHARACTERIZED BY AN AVERAGE HOLDUP TIME OF THE HYDROCARBONS AT A TEMPERATURE ABOVE 350* F. OF LESS THAN 10 MINUTES. 